Capillary electrophoretic separation techniques find wide application in the biologically related sciences. Molecular species such as peptides, proteins, oligonucleotides, and oligosaccharides are separated by causing them to migrate in a buffer solution under the influence of an electric field. The separation is normally carried out in thin-walled, narrow-bore capillary tubes to minimize the evolution of heat during electrophoretic separation, which would cause zone deformation.
Among the other mechanisms that can cause zone deformation are non-uniform electroendosmosis and adsorption to the inner surface of the capillary of the substances to be separated. However, the problems associated with adsorption and non-uniform electroendosmosis can be overcome by coating the inner wall of the electrophoresis tube with various polymeric substances.
In U.S. Pat. No. 4,680,201, Hjerten discloses a method for coating the inner wall of a narrow bore capillary with a monomolecular polymeric coating of polyacrylamide bonded to the capillary wall by means of a bifunctional reagent, e.g., .gamma.-methacryloxypropyltrimethoxysilane. These capillaries can be used for free-zone electrophoresis in open tubes.
Novotny et al., U.S. Pat. No. 5,074,982, discloses that the inner wall of silica capillaries used in electrophoretic separations can be coated with bifunctional reagent using a Grignard reagent, for hydrolytic stability.
Holloway, U.S. Pat. No. 5,110,439, shows a polyacrylamide gel electrophoresis column having a fused silica tube, a polyacrylamide gel matrix, and chains of non-crosslinked polydimethylsiloxane radially between and covalently attached to both the tube and the gel matrix.
Huang et al. (J. Microl. Sepns. 4:135-143, 1992) reports a procedure for bonding polyethylene glycol and polyethylene imine onto the surface of a microcapillary tube. The capillary surface is first treated to create a uniform, dense distribution of silanol groups for bonding of a silicon hydride polymer. At elevated temperature, e.g., 250.degree. C., the Si--H groups in the polymer mixture reacted with the silanol groups on the capillary surface and remaining Si--H groups crosslinked polymer chains. Free-radical reactions through Si--CH.sub.3 groups further crosslinked the polymer chains.